1. Field of the Invention
The present invention is broadly concerned with improved, low pH aqueous polymer mixtures containing polymers having anionic (e.g., carboxylate) functional groups, and the use of such mixtures in or with liquid or solid fertilizer materials containing ammoniacal nitrogen, so as to reduce the extent of nitrification of the ammoniacal nitrogen when applied to soils. More particularly, the invention is concerned with such polymer mixtures, their metal salts or complexes, fertilizer products and methods, wherein the selected polymers or polymer derivatives are substantially water dispersible, carboxylated copolymers, most preferably the partial metal salts of maleic-itaconic polymers.
2. Description of the Prior Art
Plants have been fertilized with nitrogen-containing nutrients since the dawn of organized agriculture. However, simple incorporation of various nitrogenous ingredients into the soil is inefficient and possibly detrimental (e.g., the well-known phenomenon of “fertilizer burn”). Growing plants often do not absorb a sufficiently large fraction of provided nitrogen, and applied nitrogen can be lost through a variety of mechanisms such as volatilization, leaching, hydrolysis, and nitrification. The general nitrogen cycle is well known, Bundy, Soil and Applied Nitrogen, Wisconsin-Madison Extension Pub. No. A2519 (1998). Additionally, a review of current nitrogen fertilization technology provides additional details, Shaviv, Int'l. Fertilizer Industry Assn. Int'l. Workshop on Enhanced-Efficiency Fertilizers (2005).
When ammoniacal nitrogen is added to soil, it is subject to nitrification whereby soil bacteria including nitrosomonas convert the ammonium to nitrate (NO3). Thus, if ammoniacal nitrogen is not immediately taken up by plants, it will soon be converted to nitrate in appropriate soils and be subject to losses from leaching or volatilization. The nitrification process is temperature and moisture-dependent, and also is strongly affected by specific soil chemistries. The problem of nitrification has led to a variety of proposals for slowing down or eliminating the conversion of ammonium to nitrate by using nitrification inhibitors.
One prior fertilization technique involves sustained release fertilizers wherein a coating is applied to nitrogen fertilizer particles to impede or otherwise control the mass transfer of nutrients into the soil. Sustained release coatings are generally not water soluble and thus the fertilizer products are not generally suitable for use in liquid fertilizers. In addition, such sustained release coatings are relatively expensive owing to the cost of materials and reaction scheme complexity needed to prepare them.
Another technique is a use of urease inhibitors in nitrogen-containing fertilizer products, in an effort to increase fertilizer uptake and minimize volatilization losses. However, prior urease inhibitors are applicable only for a few of the many types of nitrogen fertilizers, and tend to be expensive. Moreover, the inhibitors are effective for only a few days in reducing nitrogen loss, even though the problem persists throughout the entire growing season; thus multiple applications are often required. Inhibitors are often subject to hydrolysis and are subject to storage temperature restrictions in order to retain efficacy. Finally, the inhibitor doses must be strictly controlled to reduce deleterious, plant-damaging side effects. Watson, Int'l. Fertilizer Industry Assn. Int'l. Workshop on Enhanced-Efficiency Fertilizers (2005). See also, Rozas et al., No-Till Maize Nitrogen Uptake and Yield; Effect of Urease and Inhibitor and Application Time, Agronomy Journal 91 (1999); Bundy, Managing Urea-Containing Fertilizers, Area Fertilizer Dealer Meetings (2001); and Harris, Evaluation of Agrotain Urease Inhibitor For Cotton Production in the Southeast, UGA Cotton Research Extension Report (2002).
The patent literature is also replete with teachings pertaining to fertilizer compositions. For example, U.S. Pat. No. 5,024,689 describes nitrogen fertilizers with nitrification inhibitors. U.S. Pat. No. 5,364,438 describes fertilizer formulations containing water, urea, ammonium nitrate, a phosphoric triamide urease inhibitor, and a nitrification inhibitor. U.S. Pat. No. 5,698,003 also discloses triamide-based urease inhibitors in fertilizers.
U.S. Pat. No. 6,515,090 describes a series of anionic polymers useful in fertilizers for enhancing plant growth. This patent discloses that the polymers are effective for preventing volatilization of nitrogen, but does not describe any nitrification inhibition properties or uses.
Despite this long history and abundant prior art, there exists a series of unresolved problems centered around inefficient utilization of nitrogen nutrients by growing plants. These problems are particularly acute in the context of reducing or eliminating nitrogen loss resulting from nitrification.